There were nearly 700,000 inmates with severe mental disorders admitted to U.S. jails in 1988. A major push of many advocates for mental health services to address the needs of mentally ill jail detainees is diversion from the jail to appropriate community-based mental health programs. While diversion has been put forward as a major solution to the inappropriate use of jails for mentally ill persons, little attention has been given to precisely what diversion means and what types of programs are effective. How diversion should be structured and operated to maximize its benefits for both mentally ill persons and jail administrators has never been examined. It is the goal of this research: (1) to document for the first time exactly what is being delivered across the U.S in the name of diversion; and (2) to determine which types of programs are perceived as the most effective and how perceived effectiveness varies by key program characteristics such as, jail size, program auspice, and the types of linkages that exist between the jails, the judiciary and the mental health system. These goals will be accomplished by a three-tiered research design: (1) a mail survey to all U.S. jails with a census over 50 detainees to determine how many jails have diversion programs for mentally ill jails detainees; (2) a telephone follow-up of all responding jails that indicate that they have diversion programs to assess the organization and financing of diversion services, the perceived effectiveness of the service, and descriptors of the jails itself; and (3) 36 sites visits, three from each of the 12 cells, with each of the four major geographic regions of the U.S. represented by 9 sites across the 12 cells. These site visits will gather detailed information from a range of correctional, judicial, and mental health staff associated with the diversion programs and the broader community mental health system. Ultimately, the data will be geared to determining which types of diversion programs for mentally ill jail detainees seem to work best in which types of jails for which types of detainees. With the range of actually operative programs documented and with analysis of how effective programs organize services fully described, the guidelines will be available for the first time to be applied to developing more appropriate services to respond to the catastrophic situations of the mentally ill in U.S. jails. Also, second generation research involving controlled, longitudinal studies of effectiveness can more appropriately be designed.